Apparatus for melting and casting metals



Dec. 2'7, 1966 A. DUNLOP APPARATUS FOR MELTING AND CASTING METALS Filed March 18, 1964 5 Sheets-Sheet l M -1 rmw Dec. 27, 1966 A. DUNLOP 3,293,706

APPARATUS FOR MELTING AND CASTING METALS Filed March 18, 1964 5 Sheets-Sheet 2 IAME n/ T; K

ADAM QUNLOP Dec. 27,1966 A. DUNLOP 3,293,706

APPARATUS FOR MELTING AND CASTING METALS Filed March 18, 1964 3 Sheets-Sheet 3 M/VEA/TOR ADAM Dun/L P 3 WWW- eazm United States Patent 3,293,706 APPARATUS FOR MELTING AND CASTING METALS Adam Dunlop, Rotherham, England, assignor to The Birmingham Small Arms Company Limited, Birmingham, England, a British company Filed Mar. 18, 1964, Ser. No. 352,815 7 Claims. (Cl. 22S2) This invention relates to apparatus for melting and casting metals in vacuum and especially to such apparatus embodying the principle of skull melting. In skull melting, melting is conducted in a cooled crucible, such for example as a water-cooled copper crucible, in which a skull of the metal is formed on the inner surface of the crucible and subsequent melting takes place in this skull. Skull melting is mainly used in connection with metals and alloys which are liable to react with refractory crucibles and thereby result in undesirable inclusions in the metal.

An object of the invention is to produce a relatively simple apparatus for skull melting in a semi-continuous manner.

According to a feature of the invention apparatus for the melting and casting of metals utilising the principle of skull melting comprises a crucible which is connected to a mould in such a manner that after the crucible if full of molten metal it may be tilted or rotated the mould moving with the crucible so that the mould is automatically filled Other features of the invention will become apparent from the following description of an apparatus given by way of example with reference to the accompanying drawings in which:

FIGURE 1 shows diagrammatically a side elevation of a combined melting and casting machine,

FIGURE 2 is a front elevation of the machine taken on line YY of FIGURE 1,

FIGURE 3 is a sectional view of the machine along line ZZ of FIGURE 2,

FIGURES 4 and 5 are side and front elevations showing a modified form of melting chamber, and

FIGURES 6 and 7 are similar views showing a further modified form of melting chamber.

The machine consists of four essential parts: an electrode feed mechanism, 1 an electrode chamber, 2 a melting chamber 3 and mould charging and discharging chambers 4 and 5.

An electrode feed rod 6 passes through a vacuum seal 7 into the electrode chamber 2. An electrode 8 of the alloy or metal to be melted is attached to a tungsten connector 9 which in turn is fastened to the end of the feed rod 6 in the electrode chamber 2. Admission to the electrode chamber is elfected via movable door 10. A vacuum valve 11 connects the electrode chamber 2 to the melting chamber 3.

The melting chamber 3 contains a cold crucible 12, such as water cooled copper with a clamping arrangement for fixing the crucible to the mould 13 the whole assembly being pivotable about a hollow shaft 14 carrying an electrical connection 26 to the crucible as well as the cooling water. The crucible 12 is so located that it is coaxial with the electrode 8, the axis of rotation of the combined crucible and mould assembly being so arranged that pivoting from the melting position to the casting position, as shown in FIGURE 1, can be effected without retracting the electrode. Thus there is the minimum of delay between switching off the power and casting.

On opposite sides of the melting chamber 3 are fitted a mould charging chamber 4 and a mould discharging chamber 5. These chambers are connected to the melt- 3,293,706 Patented Dec. 27, 1966 ing chamber 3 by two vacuum valves 15 and 16 and are so arranged as to be in line with the mould 13 when in the casting position 31. The outer ends of the chambers 4 and 5 are closed by movable doors 17 and 18 fitted with handling arms 19 and 20 which pass through flanges 21 and 22 connected to the doors by flexible hollows 23 and 24 permitting the necessary movement of the handling arms 19 and 20 when charging and discharging moulds.

A source of electrical power is connected in known manner through cables 25 and 26 to the consumable electrode and crucible respectively and may be alternating current although it is preferable to use direct current.

To illustrate the semi-continuous working of the machine the sequence of operations will now be described from the time a mould has been cast and withdrawn into the mould discharge chamber with the crucible assembly left in the casting position.

The three vacuum valves 11, 15 and 16 are closed, and a new mould 13 is introduced into'the mould charging chamber 4 by hanging the mould by two lugs 27 in appropriate slots 32 of the handling arm 19. The mould charging chamber 4 is then evacuated, and the vacuum valve 15 connecting the melting chamber 3 and the mouldcharging chamber 4 is then opened. The mould 13 is introduced into the melting chamber 3 for clamping to the melting crucible 12, this being efiected by pushing a rod 28 upwards to engage with a clamp screw 29 and rotating to fix the mould in the casting assembly. The rod 28 is retracted and the casting assembly is rotated into the melting position 30 (i.e. with the mould horizontal) and locked in this position. The consumable electrode 8 with a tungsten connector 9 is fitted to the end of the electrode feed rod 6 in the electrode chamber 2, the door 10 is closed and the electrode chamber evacuated. The valve 11 connecting the electrode chamber 10 and the melting chamber 3 is then opened and the electrode 8 fed into the cold crucible 12, the crucible being already lined with a skull of metal from the previous melt. With the electrical power switched on arcing occurs between the tip of the electrode 8 and the skull in the cold crucible 12 with resulting melting of the electrode. The electrode is fed in either manually or automatically to maintain the arc and build up a pool of liquid alloy or metal in the crucible, and when melting of the electrode is completed the feeding in is stopped and an arc maintained between the cooled tungsten connector 9 and the liquid in the crucible to bring the melt up to the desired temperature. When this has been attained the power supply is switched oil? and the combined crucible and mould assembly immediately rotated through 90 into the casting position 31 with the resulting rapid trans fer of metal from the crucible 12 to the mould 13. The important feature of this method of pouring is the short delay which occurs between switching off the power supply and the filling of the mould, since with any substantial delay on pouring after the power supply is cut off skull becomes undesirably thick and the pool of liquid alloy or metal too cold for satisfactory casting.

During the melting operation the previously cast mould is withdrawn from the mould-discharging chamber 5, the chamber is closed, and then evacuated.

With the combined crucible and mould assembly in the casting position 31 and the mould discharge chamber 5 already evacuated, the valve 16 connecting the mould discharging chamber and the melting chamber 3 is opened and the mould 13 removed by the reverse procedure described for charging the mould.

With the cast mould in the mould-discharging chamber, the three vacuum valves 11, 15 and 16 are closed and the sequence of operations repeated for the next melt.

In a simplified arrangement as shown in FIGURES 4 and 5, the mould charging chamber 4 and discharging chamber 5 are not used, the mould 13 being placed direct- 1y into the melting chamber 3 through a door 37 and after evacuation, melting and casting, suflicient time is allowed for the skull in the water cooled crucible 12 to cool before opening the melting chamber to remove the filled mould and recharge with a new mould. This arrangement is suitable for less reactive alloy casting which do not oxidise unduly in the solid shade when air is admitted to the melting chamber while the casting is still hot.

FIGURES 6 and 7 illustrate the alternative use of a centrifugal casting device with a machine in accordance with the invention. The mould 13 is initially attached to a rotary table 33 which is fitted with a shaft 34 terminating in a clutch arrangement 35. When the mould 13 and the crucible 12 are in the melting position 30, the clutch arrangement can be engaged by a drive shaft 36. The drive shaft 36 can be rotated by suitable means (not shown) located outside the chamber.

In operation, with the combined crucible and mould assembly in the melting position 30, the clutch 35 is engaged, and as the melt is nearing completion the mould 13 is rotated at the desired speed. When melting is complete, and the melt has attained the desired temperature, the clutch 35 is disengaged and the combined crucible and mould assembly immediately rotated into the casting position 31, with the resulting rapid transfer of metal from the crucible to the spinning mould.

Important features of the invention are the control that is possible over metal casting temperature and the speed and precision with which metal is transferred from the crucible to the mould. With cold crucible melting, particularly when small charges are being melted say in the region of 5 to 30 lbs. the volume of solidified skull to liquid alloy cast can be uneconomically high and the temperature of the liquid alloy can be too low for satisfactory casting. By the use of a tungsten connector, as described, super-heating of the melt is possible and the points of pivoting the combined crucible and mould assembly permits this to be done immediately on switching off the melting current without having to wait for the electrode feed rod to be withdrawn.

Another feature of the invention is the arrangement of metal and mould charging and discharging chambers making it possible to maintain the melting chamber continuously evacuated, thus preventing the oxidation of the skull retained in the crucible as would occur if the melting chamber had to be opened to the atmosphere at any time While the skull was hot. This would particularly apply when melting such reactive metals as titanium, chr0- mium and the like.

While in the apparatus or machine described the electrode is are melted, electron beam melting can also be used. The electron beam melting gun would be fitted into the electrode chamber 2 and on completing the melting the electron beam would be focused on to the melt in the cold crucible 12 for superheating.

I claim:

1. An apparatus for skull melting metal electrodes and for casting the molten electrode metal, said apparatus comprising housing means defining a melting chamber, a crucible disposed within said chamber, a mould detachably mounted on said crucible within said chamber and being disposed to one side of and normal to said crucible, means arranged on a stationary axis for mounting the assembly of said crucible and said mould for selective pivotal movement between angularly spaced apart melting and casting positions in said chamber, said crucible being upright in said melting position and being tilted substantially 90 in said casting position for pouring molten metal with said mould being upright and below said crucible in said casting position to receive molten metal dispensed therefrom, feed means for axially advancing the tip of an electrode to be melted into said chamber and substantially coaxially into said crucible when in its upright melting position, and means for melting the elec trode tip as it is axially advanced into said crucible, said stationary axis being so arranged with respect to the axis of electrode advancement that said crucible clears the portions of the electrode therein as said assembly is swung toward said casting position, whereby pouring of the molten metal may be effected without retracting the advanced electrode.

2. The apparatus defined in claim 1 wherein said stationary axis is laterally offset from and essentially normal to the axis along which said electrode is axially advanced, and wherein said mounting means Comprises a shaft supporting said crucible at a region disposed adjacent to the upper end thereof and on the side thereof opposite from said mould such that the axis of electrode advancement lies between said shaft and said mould when said assembly is in its melting position, said assembly being swingable downwardly and away from the electrode tip as it is advanced from its melting position to its casting position.

3. The apparatus defined in claim 2 wherein said housing means further defines evacuatable, mould charging and discharging chambers disposed on opposite sides of said melting chamber, said apparatus further comprising valve means for independently controlling communication between said melting chamber and said charging chamber and between said melting chamber and said discharging chamber, and means for inserting unfilled moulds into said melting chamber through said charging chamber and for removing filled moulds from said melting chamber through said discharging chamber, said valve means being selectively manipulatable to maintain said melting chamber continuously evacuated as moulds are inserted and removed therefrom.

4. The apparatus defined in claim 3 wherein said melting, charging, and discharging chambers are aligned along an axis extending at right angles to the axis along which said electrode is advanced by said feed means.

5. The apparatus defined in claim 1 comprising a rotatable shaft, means mounting said mould on said shaft for rotation therewith, a drive member mounted exteriorly of said melting chamber, and clutch means selectively operable to drive connect said member to said shaft to rotate said mould when said assembly is in said melting position and for disengaging said member from said shaft to allow said assembly to be swung to said casting position.

6. The apparatus defined in claim 2 wherein said shaft comprises a tubular member through which a cooling medium is introduced for cooling the walls of said crucible.

7. The apparatus defined in claim 3 comprising means disposed exteriorly of said housing means for selectively fixing said mould to and detaching said mould from said crucible.

References Cited by the Examiner UNITED STATES PATENTS 2,796,644 6/1957 Kuhn 22--73 2,806,271 9/1957 Operhall 22-73 3,108,151 10/1963 Garmy et al. 1310 FOREIGN PATENTS 73,021 8/ 1951 Denmark. 1,121,280 1/1962 Germany.

I. SPENCER OVERHOLSER, Primary Examiner.

R. D. BALDWIN, Assistant Examiner. 

1. AN APPARATUS FOR SKULL MELTING METAL ELECTRODES AND FOR CASTING THE MOLTEN ELECTRODE METAL, SAID APPARATUS COMPRISING HOUSING MEANS DEFINING A MELTING CHAMBER, A CRUCIBLE DISPOSED WITHIN SAID CHAMBER, A MOULD DETACHABLE MOUNTED ON SAID CRUCIBLE WITHIN SAID CHAMBER AND BEING DISPOSED TO ONE SIDE OF AND NORMAL TO SAID CRUCIBLE MEANS ARRANGED ON A STATIONARY AXIS FOR MOUNTING THE ASSEMBLE OF SAID CRUCIBLE AND SAID MOULD FOR SELECTIVE PIVOTAL MOVEMENT BETWEEN ANGULARLY SPACED APART MELT ING AND CASTING POSITIONS IN SAID CHAMBER, SAID CRUCIBLE BEING UPRIGHT IN SAID MELTING POSITION AND BEING TILTED SUBSTANTIALLY 90* IN SAID CASTING POSITION FOR POURING MOLTEN METAL WITH SAID MOULD BEING UPRIGHT AND BELOW SAID CRUCIBLE IN SAID CASTING POSITION TO RECEIVE MOLTEN METAL DIS- 